Researchers say Paxil and likely other antidepressants in the class of drugs called selective serotonin reuptake inhibitors (SSRIs) may improve higher levels of neuroticism and lower levels of extraversion that are commonly seen with depression.

Neuroticism is characterized as being inclined to have negative emotions such as anxiety, hostility, self-consciousness, impulsivity, and sensitivity to stress.

Extraversion refers to being inclined to have positive emotions, assertiveness, and gregariousness.

Paxil May Affect Personality

In a placebo-controlled trial involving 240 adults with moderate to severe depression, 120 patients in the study took Paxil, 60 underwent cognitive therapy, and 60 took placebos for eight weeks.

In weeks 9-16, half of the participants on placebo were given Paxil. Then there was a 12-month phase when half of those in the Paxil group stayed on Paxil and half were taken off Paxil and given placebo pills.

Personality variables and depression were monitored through the study period.

All patients showed less depression at week 8, the researchers report in the December issue of Archives of General Psychiatry.

Paxil reduced neuroticism and increased extraversion, says study researcher Tony Z. Tang, PhD. Both traits have been linked to the brain’s serotonin system, which is targeted by Paxil and other SSRIs.

Neuroticism and Extraversion

Many, if not most, people experience some of neuroticism's personality traits, including a tendency to see things in a negative light and unusual anxiety and fearfulness, one of Tang’s collaborators, Robert J. DeRubeis, PhD, of the University of Pennsylvania, tells WebMD.

In addition, he tells WebMD, the patients in the Paxil group became more extraverted, meaning they became more open to new experiences, calmer, less self-conscious, and more even-tempered.

The researchers say their findings provide evidence against a theory known as the “state effect hypothesis,” which proposes that any personality changes during SSRI treatment occur only because they alleviate symptoms of depression.

“One possibility is that the biochemical properties of SSRIs directly produce real personality change,” the researchers write. “Furthermore, because neuroticism is an important risk factor that captures much of the genetic vulnerability for major depressive disorder, change in neuroticism and in neurobiological factors underlying neuroticism might have contributed to depression improvement.”

If further research can repeat the findings, it means that “there are important and noticeable effects of the medicine that have gone undetected,” DeRubeis tells WebMD. “And the findings are consistent with the idea that the medicines work more by affecting neuroticism and extraversion ... whereas we have always thought that these personality variables, though mostly stable, go up and down as depression waxes and wanes.”